In the field of inkjet printing, two basic inkjet processes are known. First, direct inkjet printing is known. In direct inkjet printing, droplets of ink (or any other liquid) are applied on a recording medium, i.e. the recording medium on which the ink is to be applied to form a resulting printed image. The recording medium is output by the inkjet printing assembly.
Second, indirect inkjet printing is known. Indirect inkjet printing is also known as intermediate inkjet printing. In indirect inkjet printing, in a first step, the ink or other liquid is applied in droplets on an intermediate medium such as a rotating belt, for example. In a second step, the ink on the intermediate medium is transferred to the recording medium. The intermediate medium may be re-used or discarded.
While direct inkjet printing is a simple printing process suitable for applying ink on any kind of substrate as a recording medium, the actual quality and robustness of a printed image varies strongly with the kind of substrate used. Depending on the interaction between substrate and ink, the ink may flow too much or too little or may spread in different directions due to structure of the substrate (e.g. paper fibers). Ink droplets may show coalescence resulting in (color) bleeding, and the like. In practice, an inkjet printing assembly is designed and configured to be used in combination with a small number of kinds of substrates, since it is virtually impossible to provide for a good print quality on every kind of substrate. Further, adherence to a substrate is also very much dependent on the interaction between substrate and ink. So, even if a good image quality is obtained, it may be that the printed ink is (too) easily removed from the substrate again.
In indirect inkjet printing, the above mentioned challenges of direct inkjet printing may be removed by use of a predefined intermediate medium having a priori known properties and interaction with the ink. An image is build on the intermediate medium, wherein the properties of the intermediate medium may even have been designed and configured for optimal image building from droplets of ink expelled from an inkjet print head. In another embodiment, a specific process liquid may be applied to adapt or optimize the interaction of the droplets on the intermediate medium. The image thus build on the intermediate medium is then transferred as a whole to the recording medium, wherein the ink may have been processed prior to the transfer to prevent undesirable effects upon transfer. For example, the ink may have been partially dried, such that only a small amount of solvent (such as water in case of an aqueous ink) is received on the recording medium preventing undesired deformation of the recording medium due to an excessive amount of solvent being absorbed. On the other hand, a transfer yield, i.e. a ratio of an amount of ink actually transferred and an amount of ink present on the intermediate medium, may differ between different recording mediums.
In general, dependent on the application and/or desired printed image properties and/or the kind of recording medium and/or other aspects, the direct inkjet process may be preferred or the indirect inkjet process may be preferred. Moreover, even with the same recording medium, sometimes the direct inkjet transfer may be preferred, while at another time, the indirect inkjet process may be preferred.
It is an object of the present invention to provide for a hybrid inkjet printing system that is enabled to selectively apply the direct inkjet process and the indirect inkjet process.